I think it's mainly due to Flowers returning, an experienced OL, and the idea that Strong can improve the defense enough and that he was successful before at Louisville. Throw in one of the easiest schedules since, well, Western Michigan last year and the fact that the West is much better and USF is a safe bet for most of these folks.
Problem is, that defense was horrible last year and Strong didn't exactly make UT's defense respectable during his tenure. They're also bringing in the Briles' offense so it'll be interesting to see how their players, especially Flowers, handles it. They also lost their top RB, Marlon Mack, who was a big reason for their success.
They'll be successful because of their schedule, but those last three games against UH, Tulsa and UCF may be tougher than a lot of folks are predicting.